1. Field of the Invention
The present invention relates to an image display control apparatus, and, more particularly, to an image display control apparatus which uses first through third image memories to accomplish predetermined screen effects.
2. Background of the Invention
Recently, the standardization of high definition still picture disks has been attempted. FIG. 1 presents a block diagram showing the fundamental structure of a system which handles such a disk.
Referring to FIG. 1, an image drive unit 1, an audio drive unit 2 and a control drive unit 3 access respective disks on which image data, audio data and control data are respectively recorded, and send read-out signals to a player 4.
The image data read out by the image drive unit 1 is supplied to the input terminal of a selector 5, which serves to selectively switch the output destinations for the input data received at its input terminal. The selector 5 has a first output terminal connected to the input terminal of a compression decoder 6 and a second output terminal connected to the input terminal of a selector 7 as well as the output terminal of the compression decoder 6. The compression decoder 6 has a decoding function with JPEG (Joint Photographic Expert Group: an international standard for compression of information of a still picture) base-line compression. The selector 7, which serves to selectively switch the output destinations for the data received at its input terminal, has first, second and third output terminals respectively connected to image memories 8a, 8b and 8c.
The image memories 8a to 8c as a whole have a 3-frame structure in order to exhibit predetermined effects, and are respectively treated as first, second and third memories each for one frame. In this respect, those image memories 8a to 8c are called "first, second and third frame memories". The output data of each of the three image memories is supplied to a screen effect controller 9 where it is subjected to predetermined screen effect control, such as cutting, dissolving, wiping, roll switching, continuous scroll or program wiping that involves data transfer between memories as its premise. The resultant signal is then supplied as an image signal to a CRT 10 as a display device.
The audio data read out by the audio drive unit 2 is subjected to predetermined signal processing in the player 4 to drive loudspeakers 11L and 11R. The control data read out by the control drive unit 3 is used in the player 4 for some control or the like to present predetermined screen effects. The operation of those individual devices described above is controlled by a control apparatus (not shown).
In this system, the mode is specified by the control data or through a manual operation to accomplish predetermined screen effect control. In the case where a continuous vertical scroll instruction is issued, one mode of the predetermined screen effect control, all of the first through third frame memories are used. This case will be discussed below more specifically.
The individual frame memories 8a, 8b and 8c constitute one memory space as shown in (a) in FIG. 2, with different pieces of image data stored in the respective frame memories. In the case where every piece of the image data in a broken lined frame d as a display area, or every piece of the image data stored in the first frame memory 8a is transferred from the screen effect controller 9 to the CRT 10 and is displayed thereon, when screen effect control corresponding to the continuous vertical scroll instruction is performed, the broken lined frame d moves to an area in the second frame memory 8b as shown in (b) in FIG. 2 so that part of the image data of the first frame memory 8a and part of the image data of the second frame memory 8b are displayed at the same time. When the continuous vertical scroll continues, the broken lined frame d moves further down in the diagram so that all the image data of the second frame memory 8b is displayed as shown in (c) in FIG. 2.
When the broken lined frame d leaves the area of the first frame memory 8a as shown in (c) in FIG. 2, image data supplied based on the image information from the image drive unit 1 is stored in the first frame memory 8a as image data to be displayed next. At the time, if the continuous vertical scroll continues, the broken lined frame d moves further down in the diagram so that part of the image data of the second frame memory 8b and part of the image data of the third frame memory 8c are displayed at the same time as shown in (d) in FIG. 2.
Then, when the broken lined frame d moves further down as shown in (e) in FIG. 2, all the image data of the third frame memory 8c is displayed and new image data is stored in the second frame memory 8b. When the downward movement of the broken lined frame d continues to be in the state shown in (f) in FIG. 2, part of the image data of the third frame memory 8c and part of the image data of the first frame memory 8a are displayed at the same time. Then, the broken lined frame d returns to the aforementioned state shown in (a) in FIG. 2 if the continuous vertical scroll is effective. Thereafter, the operational sequence from (a) to (f) in FIG. 2 is repeated until the continuous vertical scroll is disabled.
In executing continuous vertical scroll, the conventional apparatus needs three frame memories as described above.
There may be a case where other screen effect control than the predetermined one in the above system is executed during such continuous vertical scroll, e.g., where a user tries to accomplish the desired screen effect control with arbitrary image data the user has called to hold. In such a case, to store the necessary image data, a separate frame memory besides the first to third frame memories should be provided. Such need of additional memory is thought to be unsatisfactory in view of reducing the memory capacity and improving the cost performance.